Fiber-optic connectors of various styles have been employed to terminate fiber-optic cables and facilitate their connection to other fiber-optic cables. A standard fiber-optic connector specification known as DIN 47256 has been adopted by the industry, which places certain design limitations on the size and configuration of connectors built in conformance with the DIN 47256 specification. One specification requires that the coupling nut of the connector have an outside diameter of no larger than seven millimeters. The connector typically uses a ceramic or metal ferrule with an outer diameter of 2.5 millimeters.
In the past, fiber-optic connectors built according to the DIN 47256 specification did not utilize a spring-loaded ferrule arrangement. Those fiber-optic connectors that have used a spring-loaded ferrule arrangement utilized designs which are not compatible with the limitations imposed by the DIN 47256 specification.
The typical fiber-optic connector made according to the DIN 47256 specification used a rigid ferrule arrangement. Fiber-to-fiber contact is desired when two fiber-optic connectors are interconnected using a mating adaptor so that the optic fiber extending through the one ferrule and terminating at its ferrule tip will be positioned immediately adjacent to the optic fiber which extends through the other ferrule and terminates at its ferrule tip.
The conventional adaptor is exteriorly threaded along its length and has a central passageway extending fully therethrough sized to receive the ferrules of the two connectors being interconnected so that the ferrules are in substantial coaxial alignment. Each end of the adaptor has a shoulder which engages and seats against a corresponding shoulder of the connector when the connector coupling nut is fully threaded onto the adaptor. Preferably, when the coupling nuts of the two connectors are tightened onto the opposite ends of the threaded adaptor, the shoulders of the adaptor will firmly seat against the corresponding shoulders of both of the connectors with the tips of the two ferrules being in contact.
If the dimensions of the adaptor and the two connectors are not precisely matched, an undesirable optical and mechanical connection is achieved. Either the ferrule tips are not brought into contact and a space results therebetween, or the ferrule tips are in contact but the adaptor shoulders are not firmly seated against the corresponding connector shoulders.
When a space exists between the ferrule tips, and hence the two optic fibers, both insertion loss (also called "signal through loss"), and return loss (also called "signal reflected loss") are increased. These losses are reduced if the ferrule tips are brought into contact.
If the adaptor shoulders are not fully seated against the corresponding connector shoulders, a loose mechanical connection results. If the fiber-optic cable to which the connector is attached is subject to mechanical loading in a direction transverse to the axial length of the connector, the loose mechanical connector allows the ferrule to move laterally within the adaptor and thus slightly out of axial alignment with the ferrule of the other connector. When this occurs, the signal losses resulting from the misaligned ferrule tips increase, sometimes to unacceptably high levels.
These problems are substantially overcome by the use of spring-loaded ferrules, but such a design has not previously been possible while still conforming to the DIN 47256 specification.
Even existing fiber-optic connectors which do utilize spring-loaded ferrules have had their problems. As mentioned, they are bulkier than desired which increases the spacing required when positioning connectors side-by-side such as is often necessary. Another problem relates to the fact that the buffer of the cable which surrounds the optic fiber is separated from the supporting outer jacket along a long portion of its length within existing spring-loaded ferrule connectors. This often results in the bending of the buffer in the area where it is unsupported and the buckling of the optic fiber therewithin. The result of fiber buckling is increased insertion losses.
Another problem encountered in the past with fiber-optic connectors is that once the user selected a particular style of connector and installed it on a fiber-optic cable, the cable had to be cut to remove the connector if the user decided to switch to another style of connector. Presently popular connector styles, in addition to the DIN 47256 connector discussed above, include ST, FDDI, FCPC, and SC connectors.
With presently available connectors, when a user decides on a particular style connector to be initially used for the fiber-optic cables in a system, the user is locked into that connector design permanently unless the user is willing to detach all of the connectors from the cables and replace them with entirely new connectors. Such a changeover involves great cost. This cost involves not only the purchase of replacement connectors, but also the time involved in removing the old connectors, preparing the fiber-optic cable ends for the new connectors, installing the new connectors on the cable ends, and system downtime during the re-termination process. Nevertheless, this cost must frequently be incurred because the style connector initially chosen for a system is determined not to be the style of connector desired later.
Another problem encountered with presently available fiber-optic connectors is that during initial installation the connector has to be disassembled for reliable insertion of the fiber-optic cable into the connector to position the optic fiber in the connector's ferrule. This is particularly true for some connectors which utilize spring-loaded ferrules.
Yet another problem encountered with presently available fiber-optic connectors is that certain internal parts of the connector can rotate relative to each other upon assembly of the connector which sometimes results in scoring or nicking of the optic fiber or twisting the buffered optic fiber. If the optic fiber is so damaged, unacceptable transmission losses result.
It will therefore be appreciated that there has long been a significant need for a compact, fiber-optic connector manufacturable in accordance with the DIN 47256 specification which utilizes a spring-loaded ferrule, but yet avoids the fiber buckling problems experienced with other connectors using spring-loaded ferrules. There has also been a significant need for a universal fiber-optic connector which can be easily converted from one connector style to another without detaching the fiber-optic cable from the connector. Further, there exists a need for a fiber-optic connector which allows the optic fiber to be reliably inserted into the connector during initial installation of the connector on the cable without disassembly of the connector. The connector should also avoid the rotation of parts which can result in damage to the optic fiber upon assembly of the connector. The present invention fulfills these needs and further provides other related advantages.